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using glycerine in bio gas digester

Good morning Gents,

As we are hopefully moving onto our new block in the next few month, I have been trying to find a way to deal with the challenge of disposing the glycerine properly. We are going totally of grid, no sewer connection at all. Only the good old septic. Since we are using composting toilets, our septic is designed for that accordingly.

Over the weekend I had a look around and some people on the net suggested to take it to the sewer plant as they would be happy to take it for free to feed their methane digester. Being a practical curious guys as we all are on here, I had a look around and found out that it is rather easy to build your own digester and to make your own gas for cooking and possible heating/hot water.

Now the question, is there anyone here who has done or is doing just that? And if so, how much do you feed into the digester. I have read somewhere that glycerine is a high energy feed, so one must be careful not to feed to much otherwise acid forming bacteria kill the methane forming bacteria.

I figured since the pollies are threatening us with a gas shortage in the near future, prices will go up a fair bit, so making our own supply would be great.

Re: using glycerine in bio gas digester

Hi Bueff, I send my potassium glycerol to an A/D facility. As you say it is a 'high energy 'feed and the people that take mine in 1000 to 2000 litre batches are glad to have it.
When the tanker arrives to take it, it then goes to a food pre-packing plant where approx 25000 litres of liquid food waste are pumped in, so the dilution is small.

Re: using glycerine in bio gas digester

Bueff,
You would be better using the human wastes to feed the bio gas digester than using a composting toilet. This will provide the 'starter microbes' and provide some dilution for the biodiesel byproduct. Will you have neighbours with lawns, or paddocks which need mowing regularly? these wastes can be added to the digester to improve its output and further dilute the byproduct.

You will need some form of methane storage too.

Have fun.

Life is a journey, with problems to solve, lessons to learn, but most of all, experiences to enjoy.

Re: using glycerine in bio gas digester

Originally Posted by Tony From West Oz

Bueff,
You would be better using the human wastes to feed the bio gas digester than using a composting toilet.
Have fun.

Thanks Tony,

(Un)Fortunately we already have the 'side waste plan' done up and I am reluctant to pay another $1500 for the new site waste management plan, besides our system would then increase in size, the trenches have to be bigger..... you name it.

We have have just over 2 acres, so plenty of grass clippings, plus food scraps and clycerine. I don't think we would need a massive digester to produce gas for just cooking and possible hot water if the sun is not out.

Re: using glycerine in bio gas digester

Using medical grade glycerine I made glycerol triacetate. I think it's a fuel additive. It's worth more than glycerine, it's good for something, rather than being waste product. The formula I used was the Fisher Esterification (an old formula) Carboxylic acid (glacial acetic acid) plus alchol (glycerine) plus catalytic (small) quantity of sulfuric acid yields glyceryl triacetate (a fuel additive) plus three molecules of water. The money is in the junk end of the business. Glycerine by product might be synthesized into a liquid material that might be sold rather than washed down the drain. Another formula for it is acetic anhydride with catalytic quantity of concentrated sulfuric acid plus purified glycerine yields glyceryl triacetate.

Re: using glycerine in bio gas digester

Glycerine can be purified by vacuum distillation. Distill off the methanol present, then the water. Vacuum greatly reduces the boiling point of glycerine. At 760 millimeters pressure (atmospheric pressure) glycerine boiils and decomposes at 290.0 degrees celcius. At 1 millimeter vacuum pressure glycerine boils at 125.5 degrees celcius. With my eight hundred dollar (American Dollars) vacuum pump the lowest pressure I can get is 100 milliliters, at 100 millimeters pressure glycerine boils at 220.1 degrees celcius. That's still pretty hot. I burned an expensive piece of equipment (heating mantel) partially from getting it too hot. But foaming is possible in vacuum distillation. I don't know if the byproduct will foam up, over the still head. The boiling flask must have thick walls or it can implode. And washing out the boiling pot every time would be necessary (stainless steel?). But medically pure glycerol can be sold for something, it's not waste. It takes some practise to run a vacuum still, doing vacuum distillation.

Re: using glycerine in bio gas digester

What is the decomposition formula? 290 isn't really hot if you are burning something in open air even and since it is a lousy fuel it doesn't have any possibilities in a furnace type burner but perhaps with something else or a catalyst or are we stuck with bugs?

Re: using glycerine in bio gas digester

Years ago my great uncle had a blowtorch. It was a canister with a variable release valve that used a combustible liquid . We used kerosene in it, but if it was modified glycerin might work. It sprayed kerosene through a heated tube with several vent holes drilled through it. It heated the kerosene above room temperature so there was no soot produced from the flame. If kerosene burns just off a simple wick , soot is produced. Heating the glycerin hot prior to burning might serve to cause it to be a better fuel , or mixing it with some alcohol that it's miscible with. Like dissolves like. Glycerin is a tri-ol a triple alcohol, so is should be miscible with methanol , industrial ethanol and maybe isopropanol (2-propanol). If a person were to distill medical grade glycerine from glycerine by product from biodiesel then potassium hydroxide would likely be the better catalyst to use since it would be a liquid at a lower temperature than sodium hydroxide. Distilling glycerine from solid glycerine by product would be more of a challenge to do.